A handgun is a firearm designed to be held and operated by one hand. This characteristic differentiates handguns as a general class of firearms from long guns such as rifles and shotguns (which are mounted against the shoulder).

Major handgun subtypes are the revolver and pistol; other subtypes include derringers, single-shot pistols, semi-automatic pistols, pepperboxes, and machine pistols.

The overlapping variations in meaning of the words "pistol" and "handgun" are discussed below.

Although handgun use often includes bracing with a second hand, the essential distinguishing characteristic of a handgun is its facility for one-handed operation.

Multiple senses of the word "pistol"

The word "pistol" is often synonymous with the word "handgun". Some handgun experts make a technical distinction that views pistols as a subset of handguns. Sometimes in American usage, the term "pistol" refers to a handgun having one chamber integral with the barrel, making pistols distinct from the other main type of handgun, the revolver, which has a revolving cylinder containing multiple chambers. But UK/Commonwealth usage often does not make this distinction. For example, the official designation of the Webley Mk VI was "Pistol, Revolver, Webley No. 1 Mk VI", and the designation "Pistol No. 2 Mk I" was used to refer to both the Enfield Revolver and the later Browning Hi-Power semi-automatic.

Handheld firearms were first made in China where gunpowder was first developed. They were hand cannons (although they were not necessarily fired from the hand, but rather at the end of a handle). By the 14th century, they existed in Europe as well. The first handheld firearms that might better be called "pistols" were made as early as the 15th century, but their creator is unknown. By the 18th century, the term came to be used often to refer to handheld firearms. Practical revolver designs appeared in the 19th century, but it was not until the mid-twentieth century that the (sometimes-observed) differentiation in usage of the words "pistol" and "revolver" evolved among some speakers and the use of "handgun" became prevalent. Previously there had been no such differentiation, and in fact Samuel Colt's original patent was for a "revolving-breech pistol." There is no literal equivalent for "handgun" in the Romance languages, which continue to use cognates of the word "pistol".